Yes I can confirm that if you never accepted the gift on an alt, it is still in your mailbox.
You can then wrap it in:
Red Ribboned Wrapping Paper - Item - World of Warcraft
Once it is wrapped, you can mail it to anyone, they can accept it, unwrap it, and use it.
If you go through a zoning screen (portal, log out, join BG) or anything of that nature, EVEN if it is wrapped when you zone, it will disappear. I would suggest wrapping it and then mailing it before zoning, I think the only safe place for it to be is in our mailbox (wrapped in paper that is)
Death will not make it disappear (even when it is unwrapped)
Thanks OP!
Edit: Oh and I can confirm I am getting the 8% buff.